This invention relates to stereophonic signal demodulation circuits, and more particularly to an FM multiplex (MPX) stereophonic signal demodulation circuit.
Heretofore, a double balanced type demodulation circuit comprising differential amplifiers has been employed as an FM MPX stereophonic signal demodulation circuit. In this conventional demodulation circuit, the differential amplifiers are cascade-connected in a two-stage state, and therefore the power supply utilization factor is low. It is impossible to increase the dynamic range. Furthermore, since the signal distortion of the differential transistors in the stages are superposed, it is difficult to reduce the distortion factor. In addition, because of the unbalance in characteristic of the differential transistors, distortion occurs, and the right and left channel signals become different in level.
Moreover, for muting operation in selecting an FM broadcast station, it is necessary to provide a particular muting circuit in the rear stage of the double balance type demodulation circuit.
Thus, the conventional demodulation circuit suffers from various difficulties as described above.